The previous GAPK implementation was represented as a single
executable. So, all audio transcoding operations were available
only by calling the 'gapk' binary. This approach didn't allow
external applications to benefit from using GAPK API directly.
Since there are some projects (such as GR-GSM and OsmocomBB),
which are potential users of GAPK code base, it would be better
to have all transcoding functions within a shared library.
So, this change separates the common code into a shared library,
named 'libosmogapk', and links the 'gapk' binary against one.
Currently there are no shared headers, pkg-config manifest and
the export map, but they will be done latter.
The RTP EFR payload is a bit like the FR payload: one nibble magic
marker, then followed by the actual codec bits. So we need to
add/remove that magic marker and shift the remainder by one nibble.
After merging this change, there is support for the AMR codec (by means
of libopencore-amr, which is already used for EFR).
In terms of gapk formats, we introdude
* the "amr-opencore" format, which serves both as the canonical format,
and as the input format to opencore-amrnb itself.
* the "rtp-amr" format, which is the payload of RFC4867 octet-aligned mode
You can use the following command for a real-time RTP playback for AMR
frames:
./gapk -I 0.0.0.0/30000 -f rtp-amr -A default -g rawpcm-s16le
Since automake 1.13 INCLUDES is depricates and causes a warning
Inspired from similar patches by Alexander Huemer for other osmocom
projects
Signed-off-by: Sylvain Munaut <tnt@246tNt.com>
Instead of having only file-based I/O, this enables gapk to receive and
send RTP streams, e.g. from live GSM network equipment like
sysmoBTS/nanoBTS.
Support is currently simplistic. On transmit, there is hard-coded codec
type of full-rate GSM. On receive-side, we should auto-detect the
format based on frame size and/or payload type, but we don't do that yet
at all.
Vadim Yanitskiy
Harald Welte
Sylvain Munaut